Phosphates (PO4) are the main algae nutrients (algae nutrient No. 1) in ponds. This filter material binds phosphates and thus deprives the algae of their nutritional source. The phosphates come from fish food, dead pond plants and dead algae. After undergoing an algae control process, the dying algae release the phosphates bound in them and thus fertilize the next generation of algae. The binding of phosphates at this stage is vital!
This way to the product with further additional information: JBL PhosEX Pond Filter .
You will find interesting facts about algae control in the garden pond in the Themeworld Pond: Combater as algas .